Recent Developments of Ruthenium Complexes for Dye-Sensitized Solar Cells

Almost forty years ago, dye-sensitized solar cells (DSSCs) appeared as a promising route for harnessing the energy of the sun and for converting it into electricity. In the following years, a huge number of studies have been dedicated to increase the global photovoltaic efficiencies and stability of DSSCs. Thiocyanate ruthenium complexes bearing chelating nitrogen donor ligands turned out to be among the best performing photosensitizers. In the last 15 years, a lot of work has also been dedicated to the preparation of efficient thiocyanate-free Ru dyes. In this review, these two families of ruthenium(II) complexes are presented: (a) dyes presenting thiocyanate ligands and (b) thiocyanate-free dyes. The coverage, mainly from 2021, is not exhaustive, but exemplifies the most recent design approaches and photovoltaic properties of these two classes of Ru(II) photosensitizers.